A variable-resistance memory stores different data based on different resistance. For example, a low resistance value may represent “0”, and a high resistance value may represent “1”. In general, different data, which is written to the variable-resistance memory, may correspond to different writing operations of the variable-resistance memory.
For example, when writing “0” (which is represented by a low resistance), the variable-resistance memory may perform the low resistance during the writing operation. In such cases, the variable-resistance memory usually makes the current below the clamping current to control the resistance of the component in the variable-resistance memory. In general, the resistance of the component is controlled by the voltage on the word line (WL), but the clamping current may change due to the process variation of the transistors.
On the other hand, when writing “1” (which is represented by a high resistance), the voltage on the word line should be controlled carefully. If the voltage on the word line is too low, then the writing operation may fail or perform the resistance which is too low. If the voltage on the word line is too high, then the components in the variable-resistance memory may be damaged, which causes the malfunction of the variable-resistance memory. In general, when writing “1” (which is represented by a high resistance) to the variable-resistance memory, it usually protects the circuit by performing the writing-verification operation. For example, the writing-verification operation may verify the variable-resistance memory. If the data is not written into the variable-resistance memory successfully, then the writing-verification operation increases the voltage on the word line and performs the writing operation again. The verification and the writing operation of the writing-verification operation are executed repeatedly until the verification shows that the data is successfully written into the variable-resistance memory. The writing-verification operation described above may spend extra energy and operation time.